Alkoxyalkanoic acids are useful as anionic detergents. These acids, being composed of only the elements C, H and O, do not pose the environmental problems that other detergents containing heteroatoms such as N, S, and P pose. Commercially, the alkoxyalkanoic acids are prepared in a two-step process of first reacting an alkoxyalkanol with sodium and then reacting the resultant alkoxide with the sodium salt of chloroacetic acid.
It is also known to convert alkoxyalkanols such as methyl carbitol to the corresponding carboxylic acids by oxidizing them with nitric acid. However, not all of the nitric acid can be separated by distillation, and the reaction product contains nitric acid, which is corrosive and therefore undesirable. In addition, cleavage of the ether linkages occurs to a large degree during this process.
Japanese Patent No. 50-96516, issued Jul. 31, 1975, discloses a process for the preparation of carboxylic acid salts by the liquid phase dehydrogenation of alcohols with caustic alkali in the presence of precious metal catalysts, including palladium. This process uses a relatively high temperature, 100.degree. C.-270.degree. C. These high temperatures can degrade the ether linkages especially in the highly ethoxylated alcohols.
It is known to use nitroxyl radicals/oxoammonium salts in the oxidation of primary alcohols to produce aldehydes and acids and secondary alcohols to ketones. Journal of Organic Chemistry, vol. 52 (12), pp. 2559-2562; Pure and Applied Chemistry, vol. 62(2), 1990, pp. 217-222; Journal of Organic Chemistry, vol. 55, 1990, pp. 462-466. The primary products produced in these processes are aldehydes.
It is generally more difficult to oxidize alkoxyalkanols than alkanols as it is difficult to oxidize alkoxyalkanols without splitting the molecular chain at the ether linkage and thereby produce a large proportion of undesired by-product. It is therefore an object of this invention to produce alkoxyalkanoic acids in high yields and with high selectivities from alkoxyalkanols without producing large amounts of other products such as aldehydes.
It is a further object of this invention to provide a process for the preparation of alkoxyalkanoic acids in which highly corrosive, difficult to separate, side-products are not formed.
It has been found that alkoxyalkanoic acids can be produced in high yields and with high selectivities by using catalytic amounts of a stable free radical nitroxide.